Firebase检索数据失败。

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英文:

Firebase Retrieve Data Failed

问题

我遇到了这个错误：

  1. java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.posinventory/com.example.posinventory.Bill}: java.lang.NullPointerException: Attempt to invoke virtual method 'com.google.firebase.database.DatabaseReference com.google.firebase.database.FirebaseDatabase.getReference(java.lang.String)' on a null object reference

我发现当我尝试将以下代码添加到我的代码中时出现了这个错误：

  1. di = mDatabase.getReference("transaction").child("Bill").child(id);

这是从Transaction子节点Bill数据库获取数据的整个代码：

  1. public class Bill extends AppCompatActivity {
  2.     // ... （这里省略了一部分变量声明）
  4.     @Override
  5.     protected void onCreate(Bundle savedInstanceState) {
  6.         super.onCreate(savedInstanceState);
  7.         // ... （这里省略了一部分界面初始化的代码）
  9.         // 初始化 Firebase 数据库
  10.         mDatabase = FirebaseDatabase.getInstance();
  12.         // ... （这里省略了一部分界面元素的初始化代码）
  14.         // 获取 info 数据
  15.         du = mDatabase.getReference("info");
  16.         du.keepSynced(true);
  17.         du.addListenerForSingleValueEvent(new ValueEventListener() {
  18.             @Override
  19.             public void onDataChange(DataSnapshot dataSnapshot) {
  20.                 // ... （这里省略了一部分处理 info 数据的代码）
  21.             }
  23.             @Override
  24.             public void onCancelled(DatabaseError error) {
  25.             }
  26.         });
  28.         Intent intent = getIntent();
  29.         String id = intent.getStringExtra("key");
  30.         // 获取 transaction 数据
  31.         di = mDatabase.getReference("transaction").child("Bill").child(id);
  32.         di.keepSynced(true);
  33.         di.addListenerForSingleValueEvent(new ValueEventListener() {
  34.             @Override
  35.             public void onDataChange(DataSnapshot dataSnapshot) {
  36.                 // ... （这里省略了一部分处理 transaction 数据的代码）
  37.             }
  39.             @Override
  40.             public void onCancelled(DatabaseError error) {
  41.             }
  42.         });
  43.     }
  44. }

Firebase 数据库截图：

Firebase检索数据失败。

英文:

I get this error:

  1. java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.posinventory/com.example.posinventory.Bill}: java.lang.NullPointerException: Attempt to invoke virtual method 'com.google.firebase.database.DatabaseReference com.google.firebase.database.FirebaseDatabase.getReference(java.lang.String)' on a null object reference

and I found out that when I try to add di = mDatabase.getReference("transaction").child("Bill").child(id); into my code.

This is the whole code to get data from Transaction child Bill database

  1. public class Bill extends AppCompatActivity {
  2.     TextView ph1, ph2, storename, storeaddr, transid, dlnum, date, gst, ptname, age, docname, totamt, name;
  3.     TextView medname[], unit[], batch[], qty[], rate[], exp[], amt[];
  4.     String ids[];
  5.     private DatabaseReference du;
  6.     private DatabaseReference di;
  7.     private FirebaseDatabase mDatabase;
  10.     @Override
  11.     protected void onCreate(Bundle savedInstanceState) {
  12.         super.onCreate(savedInstanceState);
  13.         requestWindowFeature(Window.FEATURE_NO_TITLE);
  14.         this.getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,
  15.                 WindowManager.LayoutParams.FLAG_FULLSCREEN);
  16.         setContentView(R.layout.invoice);
  17.         getSupportActionBar().hide();
  19.         ph1 = (TextView) findViewById(R.id.ph1);
  20.         ph2 = (TextView) findViewById(R.id.ph2);
  21.         storename = (TextView) findViewById(R.id.storename);
  22.         storeaddr = (TextView) findViewById(R.id.storeaddr);
  23.         transid = (TextView) findViewById(R.id.transid);
  24.         dlnum = (TextView) findViewById(R.id.dlnum);
  25.         date = (TextView) findViewById(R.id.date);
  26.         gst = (TextView) findViewById(R.id.gst);
  27.         ptname = (TextView) findViewById(R.id.ptname);
  28.         age = (TextView) findViewById(R.id.age);
  29.         docname = (TextView) findViewById(R.id.docname);
  30.         totamt = (TextView) findViewById(R.id.totamt);
  31.         name = (TextView) findViewById(R.id.name);
  33.         medname = new TextView[4];
  34.         qty = new TextView[4];
  35.         amt = new TextView[4];
  37.         ids = new String[] { "medname", "qty", "amt" };
  38.         for (int j = 1; j <= 4; j++) {
  39.             medname[j - 1] = (TextView) findViewById(getResources().getIdentifier(ids[0] + j, "id", getPackageName()));
  40.             qty[j - 1] = (TextView) findViewById(getResources().getIdentifier(ids[1] + j, "id", getPackageName()));
  41.             amt[j - 1] = (TextView) findViewById(getResources().getIdentifier(ids[2] + j, "id", getPackageName()));
  42.         }
  45.         du = mDatabase.getReference("info");
  46.         du.keepSynced(true);
  47.         du.addListenerForSingleValueEvent(new ValueEventListener() {
  48.             @Override
  49.             public void onDataChange(DataSnapshot dataSnapshot) {
  50.                 GenericTypeIndicator<Map<String, String>> genericTypeIndicator = new GenericTypeIndicator<Map<String, String>>() {
  51.                 };
  52.                 Map<String, String> map = dataSnapshot.getValue(genericTypeIndicator);
  53.                 name.setText(map.get("name"));
  54.                 storename.setText(map.get("storename"));
  55.                 dlnum.setText(map.get("tin"));
  56.                 storeaddr.setText(map.get("addr"));
  57.                 ph1.setText("Ph: " + map.get("ph1"));
  58.                 ph2.setText("Ph: " + map.get("ph2"));
  59.                 gst.setText(map.get("gst"));
  60.             }
  62.             @Override
  63.             public void onCancelled(DatabaseError error) {
  64.             }
  65.         });
  67.         Intent intent = getIntent();
  68.         String id = intent.getStringExtra("key");
  69.         di = mDatabase.getReference("transaction").child("Bill").child(id);
  70.         di.keepSynced(true);
  71.         di.addListenerForSingleValueEvent(new ValueEventListener() {
  72.             @Override
  73.             public void onDataChange(DataSnapshot dataSnapshot) {
  74.                 GenericTypeIndicator<Map<String, String>> genericTypeIndicator = new GenericTypeIndicator<Map<String, String>>() {
  75.                 };
  76.                 Map<String, String> map = dataSnapshot.getValue(genericTypeIndicator);
  77.                 totamt.setText(map.get("gtotamt"));
  78.                 date.setText(map.get("gdate"));
  79.                 String items = map.get("gitems");
  80.                 StringTokenizer st = new StringTokenizer(items, "®");
  81.                 int k = -1;
  82.                 while (st.hasMoreTokens()) {
  83.                     k++;
  84.                     // Toast.makeText(Bill.this,""+k , Toast.LENGTH_SHORT).show();
  85.                     StringTokenizer sti = new StringTokenizer(st.nextToken(), "©");
  86.                     while (sti.hasMoreTokens()) {
  87.                         medname[k].setText(sti.nextToken());
  88.                         qty[k].setText(sti.nextToken());
  89.                         amt[k].setText(sti.nextToken());
  90.                     }
  91.                 }
  92.             }
  94.             @Override
  95.             public void onCancelled(DatabaseError error) {
  96.             }
  97.         });
  99.     }
  102. }

Firebase Database:

Firebase检索数据失败。

答案1

得分: 0

你尚未声明getInstance()。尝试添加以下内容：

du = mDatabase.getInstance().getReference("info")

以及

di = mDatabase.getInstance().getReference("transaction").child("Bill").child(id)

我的意思是，当你遇到mDatabase时，在其后面加上getInstance()。然后告诉我更新情况。

英文:

you have not declared getInstance(). Try adding
du = mDatabase.getInstance().getReference("info") and
di =mDatabase.getInstance().getReference("transaction").child("Bill").child(id)
. I mean when you face a mDatabase add a getInstance() to it. And let me know the update.

huangapple
  • 本文由 发表于 2020年9月17日 21:50:03
  • 转载请务必保留本文链接：https://go.coder-hub.com/63939541.html
  • android
  • firebase
  • firebase-realtime-database
  • java
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